A first embodiment of a docking device (capture tool) has been developed by the applicant Deutsches Zentrum für Luft- and Raumfahrt (DLR) as early as 1996; this docking mechanism has been used in laboratory test operation at the time.
The docking device can be introduced into the jet nozzle of an apogee engine provided in each communication satellite and may be fixed at the neck of the nozzle which is the narrowest part of the jet nozzle (see E. Settelmeyer et al., Dornier Satellitensysteme GmbH and K. Landzettel, DLR, “The experimental Servicing Satellite—ESS” (especially FIG. 7), ISTS-Conference 1998, Omiya, Japan).
This docking device comprises a linkage with a cone-shaped body, the linkage being driven by a motor via an intermediate transmission. A spreader mechanism is provided concentrically around the linkage, the mechanism comprising a number of very thin rod-shaped spreading elements made of spring steel.
When the docking device is inserted through the neck of the nozzle of the apogee engine, the spring steel spreading elements abut the cone of the linkage. By withdrawing the linkage, the spreading elements are spread to a precisely defined opening angle and are then pulled back until the spread, very thin spreading elements solidly abut the inner wall of the nozzle neck.
The spring steel spreading elements, which have a diameter in the order of 2 mm, are thus extremely thin and are coated with a layer of oxide. Since the thin spreading elements solidly abut the nozzle neck, their oxide layer is damaged to an extent, especially by unavoidable vibrations of the satellite to which the space shuttle has docked, that, after long periods of solid abutment, the thin spreading elements of spring steel become cold welded to the nozzle neck due to the high surface pressure, whereby the docking device is permanently connected to the communication satellite.
DE 198 48 427 A1 describes a space shuttle with a docking device for docking to a satellite, the docking device comprising a displaceable linkage with a cone at its distal end and a spreader mechanism with spreading elements, operable from the space shuttle. At least two spreading elements are pivotally provided on a retaining part of the docking device that is concentric to the linkage. In the area of their outward directed distal ends, the curvature of the outer surface of each of the spreading elements corresponds to the curvature of the nozzle neck of the satellite engine. From U.S. Pat. No. 6,299,107 B1 it is known that spreading elements may be designed as lever spreaders.